Carbon materials

ABSTRACT

There is described a carbon material comprising sp2 and sp3 hybridised carbon. Also described is a method of making a carbon material the method comprising: exposing a substrate to a flux of at least 1011 carbon ions per cm2 of substrate per 1 ms, a majority of the carbon ions having a kinetic energy of at least 10 eV. Further, electrodes comprising the carbon material are described. The electrodes may operate as an anode in Li ion battery characterised with improved specific capacity and operation life-time.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/579,509, filed Sep. 23, 2019, which claims the benefit of GBPatent Application Ser. No. 1815535.8 filed Sep. 24, 2018, which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates to carbon materials, methods of making suchmaterials, and electrodes and electrochemical cells containing suchmaterials.

FIELD OF THE DISCLOSURE

This invention relates to carbon materials, methods of making suchmaterials, and electrodes and electrochemical cells containing suchmaterials.

BACKGROUND

In the lithium ion battery field there is a demand for electrodematerials, in particular anode materials, with high specific energy(lithium storage) capacities and cycle stabilities. Although graphiteanodes have good stability and low cost, their experimental specificcapacity is about 330 mAh/g (the theoretical maximum capacity is 372mAh/g, R. Dash, et. al., Sci. Rep. 6, 27449; doi: 10.1038/srep27449(2016)), which does not meet requirements of current and futuretechnologies, for example in the automotive area.

Si- and P-based materials are considered as promising candidates becausetheir specific capacities can reach as high as 4,200 and 2,596 mAh/g.However, they both suffer from the poor reversibility caused by a largevolume expansion >300%.

There is a continuous research for novel allotropes or forms of carbonmaterials with new or improved properties in the context of batteries.

For example, a prediction of a new two-dimensional metallic carbonallotrope was made in 2012 by Xin-Quan Wang (DOI: 10.1039/c2cp43070c).The allotrope named “net W” consists of square C4, hexagonal C6, andoctagonal C8 carbon rings and should exhibit metallic-like electricconductivity. By means of first-principles calculations the net W carbonphase was predicted to be stable. Further theoretical investigations ofthe carbon allotrope predicted that the specific energy capacity can beup to 1675 mAh/g, about 4.5 times larger than that of a commercialgraphite anode (Yu et al. in 2018—DOI: 10.1063/1.5013617).

To date there is no chemical method of synthesis of large net Wfragments.

An alternative approach to increase gravimetric capacity has been to usedisordered carbon. For example, the lithium storage capacity of hardcarbon (non-graphitizable) has been reported to be 550 mAh/g (′A newstrategy to mitigate the initial capacity loss of lithium ion batteries'—DOI: 10.1016/j.jpowsour.2016.05.063), i.e. greater than the theoreticalvalue for graphite. It has been shown that hard carbon material consistsof randomly aligned small-dimensional graphene layers (doi:10.1016/0008-6223(96)00177-7). Hard carbon generally has only sp² carbonbonds and is generally obtained by pyrolysis of organic materials. Themain disadvantage of hard carbon and related materials is a significantirreversible drop of the specific capacity during cycling compared tographite. Also, the hard carbon requires use of binder to provide anelectrical and mechanical contact to the current collector. The binderincreases the total mass of the battery with no contribution to thecapacity, hence reduces the overall energy density.

Thus, it remains a challenge to develop an anode material with highspecific energy capacity and stability during long-term cyclability.

It is an object of the present invention to address at least one problemassociated with the prior art.

SUMMARY OF THE INVENTION

From a first aspect, the invention provides a new carbon materialcomprising sp² and sp³ hybridised carbon.

From a second aspect, the invention provides a method of making a carbonmaterial, the method comprising: exposing a substrate to a flux of atleast 10¹¹ carbon ions per cm² of substrate per 1 ms, a majority of thecarbon ions having a kinetic energy of at least 10 eV.

From a third aspect, the invention provides a carbon material obtainableby the method according to the second aspect of the invention.

From a fourth aspect, the invention provides an electrode for anelectrochemical cell, the electrode comprising a carbon materialaccording to any aspect or embodiment of the invention.

From a fifth aspect, the invention provides a method of manufacturing anelectrode, the method comprising incorporating a carbon materialaccording to any aspect or embodiment of the invention into anelectrode.

From a sixth aspect, the invention provides an electrochemical cellcomprising a carbon material and/or electrode according to any aspect orembodiment of the invention.

From a seventh aspect, the invention provides the use of a carbonmaterial according to any aspect or embodiment herein in anelectrochemical cell.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, mean “including but not limited to”, anddo not exclude other components, integers or steps. Moreover, thesingular encompasses the plural unless the context otherwise requires:in particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Optional features of each aspect of the invention may be as set out inthe preceding paragraphs, in the claims and/or in the following detaileddescription, drawings and examples. Within the scope of this applicationit is expressly intended that the various aspects, embodiments, examplesand alternatives may be taken independently or in any combination. Thatis, all embodiments and/or features of any embodiment can be combined inany way and/or combination, unless such features are incompatible.

DETAILED DESCRIPTION

Some aspects of the invention relate to a carbon material. The carbonmaterial may comprise sp² and sp³ hybridised carbon and/or may beobtained by deposition of high flux, high energy carbon ions.

The term “carbon material” is used herein to refer to a materialcomprising carbon. Carbon materials may be formed essentially fromcarbon or may be doped with other species. The invention thus embracesboth undoped and doped carbon materials. Purity or composition of amaterial may, for example, be determined by Glow Discharge MassSpectrometry.

It should be noted that the exposure of carbon materials to theatmosphere generally results in the absorption of impurities such asoxygen. Thus, even undoped carbon materials will generally containspecies absorbed from the atmosphere.

Advantageously, the carbon material may contain at least 20 w % carbon,optionally at least 50 w % carbon, or even at least 80 w % carbon.Generally, an undoped carbon material might be expected to contain atleast 80 w % carbon, optionally at least 90 w % carbon, or even at leastw % carbon based on the total weight of the material. A remainder of thematerial might be made up, for example, of oxygen or other impurities.Doped carbon material might be expected to contain, for example, atleast 20 w % carbon, at least 50 w % carbon or even at least 70 w %carbon.

The carbon material may advantageously be electrically conductive in thesense that it allows the flow of an electrical current. Any detectableflow of an electric current can indicate electrical conductivity.Suitably, the carbon material may have an electrical conductivity of atleast 1 S/m, optionally at least 100 S/m, or even at least 20000 S/m.Electrical conductivity of thin films along the surface is measuredherein as illustrated in Example 12. The conductivity will depend, to anextent, on the thickness of the material being measured.

Advantageously, the carbon material may have a specific lithium storagecapacity greater than that of graphite. Specific lithium storagecapacity is defined herein as a measured value obtained from a standardcell as illustrated in Example 15. In this context, it is noted that thespecific lithium storage capacity of graphite as defined herein is about330 mAh/g.

Suitably, the initial specific lithium storage capacity of the carbonmaterial may be at least 400 mAh/g. Advantageously, the initial specificlithium storage capacity of the carbon material may be at least 500mAh/g, at least 800 mAh/g, at least 1000 mAh/g, or even at least 1800mAh/g.

The carbon material may offer a useful electrochemical cyclingstability. The term “cycling stability” is used herein to refer to theability of the carbon material to retain a specific lithium storagecapacity over multiple charge/discharge cycles of a cell.

Suitably, the carbon material may have a specific lithium storagecapacity after 200 cycles (in the standard cell illustrated in Example15) of at least 400 mAh/g, at least 500 mAh/g, at least 600 mAh/g, oreven at least 700 mAh/g.

The carbon material may advantageously offer a rapid charge and/ordischarge rate. It was found that the carbon material can show betterCoulombic efficiencies for higher cycling rates and for thicker carbonelectrodes. Embodiments of the carbon material were tested in a coincell configuration in LP30 electrolyte. A 10 μm thick carbon materialwas used to build an anode, and a commercial LiFePO₄ cathode (P/N ratio1.2) was used. A few initial cycles were required to achieve the stablecycling probably due to the solid electrolyte interface formation. Invarious embodiments, for 0.01 A/g, 0.1 A/g, 1 A/g C-rates the Coulombicefficiency was found to be 88%, 98%, and 99% respectively. The Coulombicefficiency may thus suitably be at least 80%, at least 95% and at least99% respectively for these C-rates.

Without wishing to be bound by theory, it is thought that presence ofboth sp² and sp³ hybridised carbon in the carbon material is ofadvantage. In particular, it is believed that sp² content providesadvantageous conductivity, whilst sp³ content provides advantageoushardness, which can enhance cyclability in the context of an electrode.The presence of both sp² and sp³ hybridised carbon may be inferred, forexample, based on XPS analysis.

In various embodiments, the percentage of sp²-type carbon in the carbonmaterial is at least 25 w %, for example at least 50 w %, or even atleast 75 w % based on the total weight of the carbon material.Optionally, the percentage of sp²-type carbon may be at most 90 w %, forexample at most 85 w % or even at most 60 w % based on the total weightof the carbon material.

In various embodiments, the percentage of sp³-type carbon in the carbonmaterial is at least 2 w %, for example at least 10 w %, or even atleast 20 w % based on the total weight of the carbon material.Optionally, the percentage of sp³-type carbon may be at most 50 w %, forexample at most 35 w % or even at most 15 w % based on the total weightof the carbon material.

The percentage of sp²-type or sp³-type carbon may be determined by XPSanalysis, as exemplified in Examples 7 and 11 hereinbelow.

The morphology of the carbon material may also contribute toadvantageous properties. In various embodiments, the carbon material hasbeen characterised as having a hierarchical pore morphology. Ahierarchical pore morphology comprises three types of pores: micropores,mesopores, and macropores.

As used herein, the term “micropores” may be defined as pores having apore diameter less than about 100 nm. As used herein, the term“mesopores” may be defined as pores having a pore diameter between about100 and about 1000 nm. As used herein, “macropores” may be defined aspores having a pore diameter greater than 1 micron. Pore sizes may, forexample, be determined by analysis of SEM images, as exemplifiedhereinbelow.

The surface area of the material may advantageously be at least 1000m²/g, optionally at least 2000 m²/g or even at least 3000 m²/g. Surfacearea may be measured using standard BET analysis. In one embodiment, thestandard BET measurement provided BJH Absorption cumulative area ofpores between 1.7 nm and 300 nm diameter of 2110 m²/g withadsorption/desorption cumulative volume of the pores of 59.4 cm³/g.

The carbon material may have a disordered nanostructure. In particular,the carbon material may comprise both amorphous and crystallineportions.

In various embodiments, the carbon material comprises nanocrystals. Theterm “nanocrystals” is used herein to refer to a discrete area ofcrystallinity whose largest dimension does not exceed 100 nm. An area ofcrystallinity is an area in which the atoms of the carbon material areordered in a lattice. The nanocrystals may typically be embedded inamorphous carbon. Nanocrystals can be detected by X-Ray Diffraction(XRD) or Transmission Electron Microscopy (TEM) analysis.

In various embodiments, the carbon material may comprise areas ofregularly arranged layers of carbon. Such areas may be embedded inamorphous carbon. The areas may constitute nanocrystals or may form anetwork of layers. In various embodiments, an area may comprise singleor few-layer sheets of carbon with a regular arrangement. For example,an area may comprise in the range of from 1 to 100 carbon layers, or inthe range of from 5 to 50 layers. The layers may appear as graphene-like2D sheets of carbon that are regularly arranged.

In various embodiments, the inter-layer spacing between individuallayers in areas of regularly arranged carbon may be greater than 0.335nm (i.e. greater than the inter-layer spacing in graphite). Suitably,the inter-layer spacing may be in the range of from 0.340 nm to 0.370nm, optionally in the range of from 0.348 to 0.366 nm. In variousembodiments, the average inter-layer spacing in the areas may be in therange of from 0.345 to 0.365 nm, optionally in the range of from 0.350to 0.360 nm. Inter-layer spacing may be measured as set out in Example 8hereinbelow.

The carbon material may be a doped material. Suitably, the doped carbonmaterial may comprise in the range of from 0.1 w % to 30 w % of one ormore dopants, for example in the range of from 0.1 w % to 10 w %dopant(s), or in the range of from 0.2 w % to 5 w % dopant(s) based onthe total weight of the doped material. Examples of dopants which maymake up the doped material together with carbon include Si, P, Fe, Cu,Li, Al, N, O, S, P, B, Ti, Co, Ni, Na, Ka or any other materialincluding metals, semiconductors, polymers or gases.

The weight percentage of dopant(s) in the carbon material may, forexample, be determined by Glow Discharge Mass Spectrometry.

The dopant can provide additional functionality to the carbon materialor enhance or suppress already existing functionality. For example, Sidopant increases the specific capacity for lithium ions, while Cu dopingimproves conductivity and hardness but decreases the specific capacity.

Advantageously, the dopant may form chemical bonds with carbon, forexample as a result of co-deposition with carbon. Additionally, oralternatively, dopant may be incorporated into the carbon material asparticles or layers.

Advantageously, the carbon material may be monolithic. The carbonmaterial may form a film. Alternatively, the carbon material may beprovided in particulate form, optionally mixed with a binder.

The carbon material may be formed on a substrate. Additionally, oralternatively, the carbon material may be freestanding.

Suitably, the carbon material may form a film having a thickness of atleast 10 nm, optionally at least 1000 nm, or even at least 10 μm or atleast 50 μm.

Substrates for the carbon material may be of any suitable type.Suitably, the substrate may be a support capable of enhancing mechanicalstrength, for example to permit deployment of the carbon material in anelectrode or cell. Such a support may take a wide range of forms. Thesupport may be an internal of an electrochemical cell. For example, thesupport may comprise a monolithic surface, a membrane, grid or a fabric.

Advantageously, the substrate may comprise an electrode substrate, forexample as will be described.

Advantageously, the carbon material may bear a current collector layer.The current collector layer may comprise metal, for example a vapourdeposited layer thereof. Suitable metals include, without limitation,copper, aluminium, and lithium, and any combination thereof.

The carbon material may be obtained by suitable vapour deposition ofcarbon. Physical vapour deposition (PVD) may be employed to form thecarbon material. PVD generally involves a stream of molecules, atoms orions directed toward a substrate. This stream condenses to form asolid-state material on the substrate.

Without wishing to be bound by theory, it has been found that the carbonmaterial may be obtained by PVD with a high flux of high-energy carbonions.

Furthermore, it has been found that, on being deposited by PVD, thecarbon material may advantageously form chemical bonds with thesubstrate. The need for binders or the like to adhere the carbonmaterial to a substrate can thus be eliminated.

In various embodiments of the invention, the carbon material may beobtained by pulsed vapour deposition of carbon ions.

Pulsed Laser Deposition (PLD) and Pulsed Electron Deposition (PED) areknown forms of PVD. In these techniques a high energy density pulse froma laser or electron beam ablates a target, turning some amount of solidtarget into a plasma. This plasma expands outward, towards a substrate,in the form of a plasma plume and is deposited.

PED generally requires an electron beam source providing an electronbeam energy density of ≥10⁸ W/cm² at the target surface. Knownapparatuses and methods to produce such electron beams are based onchannel-spark discharge (CSD) techniques—see e.g. U.S. Pat. Nos.5,576,593 and 7,557,511.

Virtual cathode deposition (VCD) is a PVD technique that solves certainproblems associated with the short life-time of CSD based depositiontools used in PLD and PED. A non-limiting example of a VCD device andmethod of deposition of thin films are described in WO2016042530, whichis incorporated herein by reference.

An aspect of the invention relates a method of making a carbon materialby exposing a substrate to a flux of at least 10¹¹ carbon ions per cm²of substrate per 1 ms, a majority of the carbon ions having a kineticenergy of at least 10 eV.

Exposure of the substrate results in deposition of the carbon ions. Sucha high flux, high energy deposition has now been found to be possibleand to lead to carbon materials with advantageous properties.

The number of carbon ions per cm² of substrate may be determined by themeasuring of the ion current density with a collimated Faraday Cup.

Suitably, the flux may comprise at least 10¹² carbon ions per cm² per 1ms or even at least 10¹³ carbon ions per cm² per 1 ms. Optionally, theflux may comprise at least 10¹¹ carbon ions per cm² per 0.2 ms, or atleast 10¹² carbon ions per cm² per 0.2 ms, or even at least 10¹³ carbonions per cm² per 0.2 ms.

A majority of the carbon ions has a kinetic energy of at least 10 eV,optionally at least 15 eV, or even at least 20 eV. The energy of carbonions may be determined according to a time-of-flight method, asillustrated in Example 2.

The carbon ions may suitably be generated by ablation of a carbongraphite target.

Suitably, the method may comprise pulsed vapour deposition of the carbonions, i.e. the flux may be pulsed. Suitably, the frequency of pulsingmay be in the range of from 1-20000 Hz, optionally 100-2000 Hz, or even100-600 Hz, such as 20 Hz-200 Hz.

Optionally, the duration of the pulses may be in the range of from0.1-1000 μs, optionally 1-500 μs, or even 20-200 μs, such as 10-20 μs.

In various embodiments, a flux of at least 10¹¹ carbon ions per cm² ofsubstrate, or at least 10¹² carbon ions per cm² substrate, or even atleast 10¹³ carbon ions per cm² substrate may be deposited in one pulse.

The total pulse energy per pulse may suitably be greater than 2.5 J, orgreater than 4 J, or even greater than 4.5 J.

The method may of course comprise depositing a plurality of pulses.Suitably, the method may comprise pulsed deposition for a period of atleast 1 second, at least 1 minute, or even at least 10 hours.Optionally, continuous deposition may be performed on a movingsubstrate.

A pulsed deposition of the carbon ions may suitably be achieved byablation of a carbon graphite target with a suitably pulsed powersource, for example a pulsed electron beam source. The pulsing of thepower source may, for example, be in accordance with the parameterslisted above. The pulsed power source may suitably be operated togenerate pulses of >15 kV voltage. The pulsed power source mayadvantageously have an internal impedance of less than 15 Ohm,optionally less than 10 Ohm, or even less than 5 Ohm.

The deposition may advantageously be performed under a vacuum, as willbe understood by those skilled in the art.

In various embodiments of the invention the method may comprise avirtual cathode deposition (VCD) process. In such a process, a virtualplasma cathode (VPC) is used as a pulsed electron beam source.

A virtual cathode deposition process may, for example, compriseproviding a hollow cathode, a substrate and a carbon target, thesubstrate and the target being located on opposite sides of the hollowcathode, supplying plasma to the interior of the hollow cathode at anend of the hollow cathode nearest the target, and supplying a highvoltage pulse to the hollow cathode, such that a virtual plasma cathodeis formed and such that the virtual plasma cathode generates an electronbeam, directed towards the target wherein a plume of ablated targetmaterial comprising the carbon ions passes through the hollow cathodetowards the substrate and is deposited thereon.

Advantageously, to support high flux, high energy deposition, the highvoltage pulse may be provided from a power source having an internalimpedance of less than 15 Ohm, optionally less than 10 Ohm, or even lessthan 5 Ohm.

The high voltage pulse may be pulsed, for example, in accordance withthe parameters listed above. The voltage of the high voltage pulse may,for example be >15 kV.

Optionally, the method may comprise depositing one or more dopants.Non-limiting examples of suitable dopant species, and optionalconcentrations, are listed above in respect of the first aspect of theinvention.

Dopant ions may be deposited using any suitable technique (e.g. PLD, PEDor VCD). The dopant ions may conveniently be deposited together with thecarbon ions, for example as part of a virtual cathode depositionprocess. This may be achieved, for example by including the dopant in atarget that is ablated to form the ions to be deposited.

Alternatively, the dopant may be deposited separately from the carbonions. A preferred method comprises generating carbon ions from a firstsource, and dopant ions from a second source, the carbon and dopant ionsoptionally being deposited together onto the substrate.

Optionally, the dopant may be added to the carbon material after carbonion deposition is complete.

In various embodiments, the dopant may be deposited using VCD (asdescribed above but with a dopant target instead of a carbon target).Suitably, the method may comprise generating carbon ions from a firstVCD source with a carbon target and dopant ions from a second VCD sourcewith a dopant target, the carbon and dopant ions optionally beingdeposited together onto the substrate.

The carbon material may advantageously be used in batteries orsupercapacitors.

Some aspects of the invention relate to an electrode for anelectrochemical cell comprising a carbon material according to, orobtained according to, any aspect or embodiment of the invention.

The carbon material may constitute a vapour deposited layer and/or maybe provided in particulate form within a binder.

The electrode may comprise an electrode substrate bearing the carbonmaterial. The carbon material may suitably have a thickness in the rangeof from 0.3-200 μm on the substrate.

The electrode substrate may comprise any suitable substrate or support.

In various embodiments, the substrate comprises a current collector. Thecurrent collector may comprise a metal, e.g. a metal foil. Suitablemetals include, without limitation, copper and aluminium.

The interface between the current collector and the carbon material maycomprise an additional interlayer. The interlayer may suitably compriseTi, Si, Al or any other material enhancing adhesion, currentconductivity or specific capacity. This may also be formed by vapourdeposition.

However, it is not essential the substrate to be a current collector.The substrate may simply comprise a (non-conducting) support.

In various embodiments, the electrode substrate comprises a polymericsupport. One example of a polymeric support is a polymeric membrane.Suitable membranes are used in the art as battery or supercapacitorseparators. Suitably, the support may comprise a multi-layerpolyolefinic membrane, e.g. comprising polyethylene or polypropylene.

Advantageously, the carbon material may bear a current collector layer.The current collector layer may comprise metal, for example a vapourdeposited layer thereof. Suitable metals include, without limitation,copper, aluminium, and lithium, and any combination thereof. A currentcollector layer is of particular benefit if the substrate isnon-conducting.

The electrode may of course comprise a connector for connecting theelectrode, in particular a current collector thereof, to an electriccircuit.

An aspect of the invention relates to a method of manufacturing anelectrode, the method comprising incorporating a carbon materialaccording to any aspect or embodiment of the invention into anelectrode.

The method may comprise depositing the carbon material by PVD, suitablyaccording to any aspect or embodiment of the invention.

The carbon material may optionally be combined with other components,such as a binder, before being incorporated into the electrode. Forexample, a particulate carbon material may be prepared and mixed with abinder before being incorporated into an electrode.

Additionally, or alternatively, the carbon material may be depositedonto an electrode substrate, i.e. a substrate that forms part of theelectrode. The electrode substrate may optionally be as hereinabovedescribed.

Preferably, the method of manufacturing an electrode comprisesdeposition of the carbon material onto a support, which may optionallybe as hereinabove defined in respect of other aspects of the invention.

In various embodiments, the carbon material may be deposited onto acurrent collector. Advantageously, a carbon material according toaccording to any aspect or embodiment of the invention may be depositedwith a method according to any aspect or embodiment of the invention asa film with thickness of 0.3-200 μm on a current collector. An exampleof a suitable current collector is copper foil. Other suitable materialsinclude those listed above.

The method may comprise depositing an interlayer between the currentcollector and the carbon material. Thus, the method may comprise vapourdepositing an interlayer onto the current collector and then depositingthe carbon material. The interlayer may suitably comprise Ti, Si, Al orany other material enhancing adhesion, current conductivity or specificcapacity.

In various embodiments, the carbon material may be deposited onto asupport, suitably a polymeric support. The method may advantageouslycomprise deposition of the carbon material on the support followed bythe deposition of a current collector.

Advantageously, a carbon material according to the first aspect ofinvention may be deposited onto a polymeric membrane with a methodaccording to any aspect or embodiment of the invention, followed byvapour deposition of a conductive material (e.g. as described above) asa current collector. In this case a reduction of the current collectorweight can be achieved due to utilising the polymeric membrane as amechanical support for the carbon material.

Advantageously, a flexible polymeric support may accommodate volumechanges of the carbon material during cycling with less stress creation.The current collector which can be deposited thinner than 10 μm, or eventhinner than 5 μm, or thinner than 2 μm, would provide additionalflexibility to the electrode. Sandwiching the active material betweenthe separator and a thin polymeric membrane advantageously allows theweight of the electrode to be reduced whilst keeping the electrode hardand flexible at the same time, improving the cyclability and decreasingthe irreversible capacity.

Advantageous electrochemical and physical properties of an electrodeaccording to any aspect or embodiment of the invention may be of use invarious devices. Electrochemical properties may comprise high specificcapacity, high surface area, hierarchical porosity, high electricalconductivity, possibility to dope the material, absence of binder. Thephysical properties are mechanical hardness, good electrical contactbetween the active material and current collector, low mass of thecurrent collector, flexible support of the active material by theseparator and current collector.

Suitably, the electrode may be used in an ion cell (e.g. lithium orsodium), a solid-state cell, a fuel cell, or a supercapacitor.

An aspect of the invention relates to an electrochemical cell comprisinga carbon material and/or electrode according to any aspect or embodimentof the invention. The electrochemical cell may be a primary or secondarycell.

The cell may comprise an anode and a cathode connected by a salt bridge,or individual half-cells separated by a porous membrane. The cell maycomprise connectors allowing an electric current to be drawn fromelectrodes of the cell. The electric current may, for example, be usedto power an electronic device or a motor, for example in an automobile.

The electrochemical cell may optionally be a lithium ion cell, a sodiumion cell, a sulphur cell, a fuel cell, or a supercapacitor.

Advantageously, carbon material may be borne by one or more internals ofthe electrochemical cell. Non-limiting examples of internals areinternal walls and separators. The internals may be non-currentcollecting. Additionally, or alternatively, the cell may comprise anelectrode including the carbon material.

Suitably, the electrochemical cell may be a lithium ion cell. Suitably,the electrode may form the anode. Alternatively, in various embodiments,the electrochemical cell may be a supercapacitor, for example a lithiumion capacitor.

An aspect of the invention relates to the use of a carbon materialaccording to any aspect or embodiment herein in an electrochemical cell,optionally an anode of a lithium ion battery. The use may be for thepurpose of achieving a specific energy capacity threshold, and/or acyclability threshold, and/or a charge or discharge speed threshold, forexample a threshold as defined anywhere herein.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, mean “including but not limited to”, anddo not exclude other components, integers or steps. Moreover, thesingular encompasses the plural unless the context otherwise requires:in particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Preferred features of each aspect of the invention may be as describedin connection with any of the other aspects. Within the scope of thisapplication it is expressly intended that the various aspects,embodiments, examples and alternatives set out in the precedingparagraphs, in the claims and/or in the following description anddrawings, and in particular the individual features thereof, may betaken independently or in any combination. That is, all embodimentsand/or features of any embodiment can be combined in any way and/orcombination, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more non-limiting embodiments of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic drawing showing an apparatus for carrying out avirtual cathode deposition process;

FIG. 2 is a series of graphs showing time-of-flight measurements of thecarbon ion plume generated in the VCD process of Example 1, taken atvarious distances from the graphite target;

FIG. 3 is a graph showing a non-normalised energy distribution of thecarbon ions generated in the VCD process of Example 1;

FIG. 4 is a series of graphs showing energy-dispersive X-rayspectroscopy (EDX) results for selected samples from Example 3. (A):Sample 3; (B): Sample 4; (C): Sample 5; (D): Sample 7;

FIG. 5 is a series of scanning electron microscope (SEM) images of thecross-section of carbon material sample C7 of Example 3;

FIG. 6 is high resolution Focused ion beam (FIB) SEM image of sample C51of Example 3;

FIGS. 7A-C are XPS spectra of the carbon material samples I-K,respectively, of Example 13;

FIG. 8A is a transmission electron microscope (TEM) image of the carbonmaterial sample of Example 8; FIG. 8B is an enlarged image of zone 1 ofFIG. 8A; FIG. 8C is a graph showing the pixel intensity along the arrowin FIG. 8B;

FIG. 9 is a Raman spectrum of carbon material sample C51 of Example 3;

FIG. 10 is a graph showing the X-ray diffraction spectroscopy (XRD)spectra of the carbon material samples C21, C22 and C23 of Example 3,along with that of an aluminium substrate;

FIG. 11 is a series of X-ray photoelectron spectroscopy (XPS) spectra ofthe carbon material samples 3, 4, 5 and 7 of Example 3;

FIG. 12 is a series of SEM images of free-standing films of a carbonmaterial sample of Example 13;

FIG. 13 is the Raman spectra of free-standing films of the carbonmaterial samples of Example 13;

FIG. 14 is a photograph of a strip of iron-doped carbon-containingmaterial with a gradually increasing of iron content along the length ofthe strip;

FIGS. 15A and B are Raman spectra of three different areas of the stripof iron-doped carbon-containing material of FIG. 14 ;

FIGS. 16A and B are graphs showing XPS analysis of the carbon (FIG. 16A)and Fe content (FIG. 16B) in areas 1, 2, and 3 of the iron-doped filmstrip of FIG. 14 ;

FIGS. 17A-B shows the outcome of the electrochemical test of Example 15.FIG. 17A is a graph showing the cyclability of the coin cell testbattery with the carbon material on copper electrode. FIG. 17B is agraph showing potential versus specific capacity of the cell; and;

FIGS. 18A and B are graphs showing the results of tests on the cyclelife of the carbon material on copper electrode as anode in a lithiumion half-cell setup.

EXAMPLES

In various embodiments, the invention provides a method of making acarbon material using a VCD process.

With reference to FIG. 1 , the VCD process comprises providing a hollowcathode, a substrate and a carbon target, the substrate and the targetbeing located on opposite sides of the hollow cathode. A plasma issupplied to the interior of the hollow cathode at an end of the hollowcathode nearest the target. A high voltage pulse is then supplied to thehollow cathode, such that a virtual plasma cathode is formed and suchthat the virtual plasma cathode generates an electron beam, directedtowards the target. A plume of ablated target material comprising carbonions passes through the hollow cathode towards the substrate and isdeposited thereon.

The VCD process thus utilizes a Virtual Plasma Cathode (VPC) as a pulsedelectron beam source. Prior to each pulse of the electron beam, a newplasma cathode is generated by fast (e.g. 100 ns) ionization of anoperational gas. The plasma cathode acquires negative high voltagepotential with respect to a target due to the application to the plasmaof a high-voltage and high-current pulse (e.g. 100-10000 ns) generatedby a Pulsed Power Generator (PPG). This causes the VPC to form in thevicinity of the target and an electron beam is extracted from the plasmaboundary. The electron beam ablates the target and then the VPC decays,leaving a space for ablated target material in the form of a plasmaplume to propagate toward a substrate, where it condenses forming acarbon material.

Repetition of the pulse, which starts with the formation of a new VPCand ends with the condensing of the target material on the substrate,allows a material to grow on the substrate with controlled growth rateand properties.

Deposited material properties, such as the crystal structure (formationof chemical bonds between the atoms of the film) or the lack of it,adhesion (formation of the bonds between the film and substrate),electrical conductivity (energy gap between conduction and valence band)and roughness (surface crystal state or structure and the number ofphases), are dependent on the target material plume plasma kineticenergy, ionization level, temperature, and density. The plasma plumeparameters in turn depend on the electron beam parameters.

Example 1—Deposition of Carbon Material

A VCD tool generally as described in WO2016042530 with reference to FIG.5 thereof was used to generate a carbon ion flux and deposit a carbonmaterial. The disclosure of WO2016042530 is incorporated herein byreference. FIG. 5 of WO2016042530 is reproduced herein as FIG. 1 .

The deposition process was performed with some key modifications of theteaching of WO2016042530. In particular, the total VCD pulse energy wasraised to >2.5 J and the pulsed power source was modified to have aninternal impedance of 10 Ohm or lower. The triggering pulse parametersand gas supply were modified to further improve electron beam focusing.This increased the overall energy density of the electrons beam on thetarget surface, which in turn improved the energy delivered to the plumeplasma and increased the kinetic energy of the deposited carbon ionsabove 20 eV. The modifications are explained below in more detail.

With reference to FIG. 1 , the apparatus 1 was provided with a graphitetarget 117 (99% purity), and an aluminium substrate 125. The chamber 127was pumped down to 10-5 mbar (10⁻³ Pa) initial pressure. Then argon gaswas introduced from sources 123, 503 to increase the pressure in thechamber up to 4·10⁻⁴-8·10⁻⁴ mbar (3·10⁻²-8·10⁻² Pa), with the gas supplyfrom source 503 providing 60% to 80% of the total gas flow.

Pulsed power source 119 had an internal impedance of 10 Ohm or lower,and was operated to generate pulses of >15 kV voltage at 20 Hz-200 Hzrepetition rate. The total pulse energy per pulse was greater than 2.5J, preferably 4 J or 4.5 J. The duration of the pulses was 10-20 μs.

When a pulse reached its maximal voltage, a trigger pulse was suppliedby the trigger pulse generators 121, 502. The trigger pulse voltageswere in the range of +5 to +15 kV and had a duration of 2 μs. A firsttrigger pulse was generated by trigger pulse generator 502 and a secondpulse by trigger pulse generator 121, with no delay between the firstand second pulses beginnings. The trigger pulse generators 121 and 502were modified to have an internal impedance of 100 Ohm and total energyof 0.05 J per pulse each. This allowed the simultaneous energy injectionfrom 121 and 502 into the initial plasma 127 increasing its temperatureand density by at least 20% compared with the previous setup of a shortnon-simultaneous trigger pulses.

The electrical pulses caused the formation of a virtual plasma cathode,which in turn generated an electron beam to ablate the target. Thedenser virtual cathode accompanied with the lower impedance of thepulsed power source led to a higher electron beam current (increase on20%) and energy density of the electron beam on the target. A plasmaplume was formed and condensed on the substrate which was placed at 20cm distance from the target. A carbon material was formed on thesubstrate.

The substrate temperature did not exceed 60° C. The deposition rate at adistance of 25 cm from the target was measured with a quartz-crystalmicrobalance (QCM) and was determined to be 0.01 nm/pulse for 4J totalenergy of the pulse.

Example 2—Characterisation of Deposition

The plasma plume ablated from the graphite target in the deposition ofExample 1 was investigated with a well-known Time-Of-Flight method, forexample described in publication D. Yarmolich et.al, Plasma Sources Sci.Technol. 17 (2008) 035002. In particular, the ion current of the plasmaplume was measured with a biased Faraday Cup at distances 30-50 cm fromthe ablation point on the target. The results are shown in FIG. 2 .

The delay of an ion current peak increase with distance was transformedto the linear velocity. The lines in FIG. 2 show the delay of theFaraday Cup (I_(FC)) depending on distance. The velocity of the plasmafront was found to be of 4.5·10⁶ cm/s and the carbon ion maximum fluxpropagated with velocity of 2·10⁶ cm/s.

The carbon ion flux (number of ions arriving to the substrate per unitof surface area per unit of time) can be estimated by integrating theFaraday Cup current over unit of time that provides the total charge ofarrived ions and dividing it by the ion charge (1.6·10⁻¹⁹ C) and thearea of the Faraday Cup current collector.

With reference to FIG. 3 , the velocity of the carbon ions can betransformed to a non-normalized Energy Distribution. Most of the ionshave an energy in the range of from 10 eV to 150 eV, and significantamount of the ions have energy above 100 eV. There is some amount of theions that have energies above 150 eV. However, Faraday Cup measurementsof the ions having an energy above 150 eV are not precise enough toquantify amounts accurately, due to the high secondary electron and ionemission.

Example 3—Deposition of Further Carbon Materials

Further depositions of carbon material were performed using VCD,generally as described hereinabove, in accordance with the parametersset out in Table 1:

TABLE 1 Example Substrate Film Thickness Pulse Energy (J) 1 Aluminium100 nm 4.5 2 Aluminium 60 nm 4.5 3 Aluminium 40 nm 4.0 4 Aluminium 0.8μm 4.0 5 Aluminium ca. 1 μm 4.0 6 Aluminium ca. 1.3 μm 4.5 7 Aluminiumca. 5 μm 4.0 C7  Free-standing ca. 10 μm 4.5 C21 Aluminium ca. 1 μm 4.5C22 Aluminium ca. 4 μm 4.5 C23 Aluminium ca. 10 μm 4.5 C51 Copper ca. 5μm 4.5

Example 4—Characterisation EDX

FIG. 4 shows energy-dispersive X-ray spectroscopy (EDX) results forsamples 3, 4, 5 and 7 from Example 3. EDX analysis of the carbonmaterial in each sample revealed the presence of three elements only:carbon (film); aluminium (substrate); and oxygen (oxide layer formed onthe aluminium substrate). The signal strength of the oxygen andaluminium decreased with increasing thickness, confirming that the filmsare pure carbon. The aluminium peaks almost disappear in the EDXspectrum for sample 7, which has the thickest layer of carbon material.

Example 5-SEM Images

FIG. 5 shows scanning electron microscope (SEM) images of across-section of sample C7.

FIG. 5 a shows two clearly distinguishable zones, which correspond todifferent growing modes of the film during VCD deposition. The uppersurface and its adjacent zone is dense and representing the initialstage of the film growth. The second one starting at—1 μm thickness fromthe upper surface is largely granular. SEM analysis shows the complexhierarchical morphology of the carbon material which consists of grainswith sizes 10-100 nm (FIG. 5 c ), 100-1000 nm (FIG. 5 b ) and above 1micron (FIG. 5 a ). Grains with the size 100-1000 nm have acharacteristic repeatable shape (see FIG. 5 b-c ). One can also estimatethe pore size between the grains that is 20-100 nm from FIG. 5 c,100-1000 nm from FIG. 5 b and above 1 micron (FIG. 5 a ).

Example 6—FIB-SEM Image

In order to check the porosity below 20 nm a (Focused ion beam) FIB SEMwas employed. FIG. 6 shows a FIB SEM image of sample C51 containing thepores in the range 1-20 nm.

Example 7—XPS and Sp²/Sp³ Hybridization Ratio

FIGS. 7 a to 7 c show XPS spectra of Examples I to K from Table 4,respectively.

A near ambient pressure (NAP) X-ray photoemission spectroscopy (XPS)system (Thermo Scientific™ ESCALAB™ 250Xi) was used for elemental andcarbon bonding analysis. The system provides the following complementarycapabilities:

-   -   X-ray photoemission spectroscopy (XPS) for chemical analysis of        surfaces under inert/UHV conditions (sensitivity to the chemical        structure near the outmost of the surface (0.5-8 nm));    -   Depth profiling x-ray photoemission spectroscopy (DPXPS) which        combines a sequence of argon ion gun etch cycles (The sputter        rate estimate: Ta₂O₅=0.1 nm/sec) with XPS analysis

XPS analysis of the free-standing carbon material films shows a ratherunusual ratio between sp² and sp³ hybridized bonds.

The significant amount of sp² bonds are in line with the TEM, Raman andXRD results suggesting the existence of ordered strands of 2D sheets ofcarbon.

Example 8—TEM Images of Carbon Material on a Copper Grid

FIG. 8 a shows transmission electron microscope (TEM) images of thecarbon material deposited on a copper grid, in accordance with thegeneral method outlined above.

STEM studies have been performed in a state-of-the-art analyticalinstrument (FEI Tecnai Osiris) designed for easy TEM imaging and fastchemical mapping in scanning transmission electron microscope (STEM)configuration using energy dispersive X-ray and electron energy lossspectroscopies (EDX and EELS) with primary beam energy of 200 keV. TEMimaging is accommodated with a Gatan UltraScan1000XP (2048 by 2048pixel) camera with high-speed upgrade. Four STEM detectors (HAADF, DF4,DF2 and BF) allow angular integration over a wide range of collectionangles and are compatible with the EEL spectrometer. EDX detectors areFEIs Super-X system employing 4 Bruker silicon drift detectors (SDD) forhigh collection efficiency (>0.9 sr solid angle) and high count rates(>250 kcps). EELS is performed using Gatan's Enfinium ER 977spectrometer with electrostatic shuttering and fast Voltage Scan Modulefor Dual EELS (sequential low-loss and high-loss spectrum acquisition)and Range EELS.

The TEM images show that there are a few nanocrystals with a size ofabout 10 nm embedded in the amorphous carbon. The nanocrystals shown inFIG. 8 a appear to represent parallel sheets of graphene or Net W oranother 2D carbon allotrope packed at the structure with the d₀₀₂spacing larger than that of graphite (0.335 nm). Five different zones ofFIG. 8 a designated by rectangles were analysed on the nanocrystals d₀₀₂spacing.

FIG. 8 b shows zone 1 of FIG. 8 a . There are clear black and whitestrips representing nine 2D carbon layers. The pixels intensity alongthe arrow shown in FIG. 8 b are shown in FIG. 8 c . Averaging thedistance between the peaks in FIG. 8 c provides the d₀₀₂ spacing for thenanocrystal in the zone 1 as 0.352 nm. The d₀₀₂ spacings obtained in thesame way of five zones selected in FIG. 8 a are shown in Table 2.

TABLE 2 Interlayer distance nm d₁ 0.352 d₂ 0.348 d₃ 0.353 d₄ 0.358 d₅0.366 average 0.355

Example 9—Raman Spectra

In order to further confirm the structure, the carbon material film wasinvestigated using Raman spectroscopy.

For Raman measurements a Renishaw Ramascope-1000 was used, with a 30 mW514.5 nm Ar excitation laser operated with the holographic Notch-filterwith cut-off at ˜150 cm⁻¹. The data collection was calibrated against asilicon standard. The instrument offers spectral resolution of 0.1 cm⁻¹and spatial resolution of 1 μm. Variable laser power levels (1-100%)were used at an integration time of 10 s. Spectra were normallycollected at 5 different randomly selected point of the sample surfacesin the range of 100-3200 cm⁻¹ Raman shift. The spectra background wassubtracted with the Bio-Rad KnowItAll software and the peaks werede-convoluted using Origin software.

All samples showed the typical structure of disordered nanostructuredcarbon. An exemplar Raman spectra with G band at around1340 cm⁻¹, D bandat around 1600 cm⁻¹ and 2D band at around 2680 cm⁻¹ of sample C51 can befound in FIG. 9 . The ratio and shape of the bands depend on the VCDparameters as well as thickness of the film. The intermixed graphiticcontent with sp² (graphitic) and sp³ (diamond) carbon bonds was furtherconfirmed by deconvolution of the first order Raman spectra.

Example 10—XRD and Allotropic Structure

FIG. 10 shows the XRD spectra in Bragg-Brentano geometry for samplesC21, C22 and C23 and Al substrate.

X-ray diffraction (XRD) was performed with a D8 Advance Brukerdiffractometer (position sensitive detector (LynxEye EX) ˜6.5% energyresolution, moving slit to reduce background scattering at low angles,best instrumental resolution ˜0.06° in 2theta & ˜0.03° in omega)equipped with Cu K α. The 2θ angle was varied with a step size of0.02-0.04°. In order to achieve reasonable intensity, long countingtimes (up to 14 s/step) were utilized. With the same intention, the useof Ni- filters was avoided.

For all samples a broad peak around 20 deg is observed that mostprobably corresponds to agglomerates of 2D carbon monolayers. The peakwas found to be shifted towards smaller angles than reported in theliterature for hard carbon (‘Mechanism of lithium insertion in hardcarbons prepared by pyrolysis of epoxy resins’, doi:10.1016/0008-6223(96)00177-7). The peak at around 26.5 deg indexed as002 of graphite-like unit cell and indicates the presence of thenanocrystals. This observation is in agreement with the TEM data.

The presence of these two characteristic peaks on the same XRD patternhas never been reported in the literature.

Example 11—XPS Spectra

The X-ray photoelectron spectroscopy (XPS) spectra for samples 3, 4, 5and 7 of Example 3 are shown in FIG. 11 . A near ambient pressure (NAP)X-ray photoemission spectroscopy (XPS) system (Thermo Scientific™ESCALAB™ 250Xi) was used.

The XPS results are in good agreement with both XRD and Raman. The filmis pure carbon, with a mixture of sp² and sp³ bonds and somecarbon-oxygen bonds were observed, however the amount of oxygen is lowercomparing to the free-standing films of example 7. The oxygen wasabsorbed after the samples were extracted from the vacuum chamber andthe free standing carbon nanomaterial absorbs more than deposited on theAl substrate.

Discussion of Examples 1 to 11

Without wishing to be bound by theory, it appears that the structuralfeatures of the carbon materials were formed due to the high kineticenergy and flux of the carbon ions during the deposition. It is positedthat the processes during the deposition may be understood as follows:

-   -   1. The pure carbon ions in significant amount (>10¹² ions per        cm² of the substrate) arrive to the substrate during short time        <50 us (see FIG. 2 ) with high kinetic energies (see FIG. 3 )    -   2. The incoming ions collide with the previously deposited film        or substrate losing their energy (usually <10 eV per collision)        so a few collisions are required before the incoming ion will        stop somewhere under the surface.    -   3. Those high-energy ions (>20 eV) are sub-planted into the        substrate or previously deposited film on a depth of few atomic        layers (see Y. Lifshitz et. all, Diamond and Related Materials        4 (1995) 318, and references within it). Lifshitz did not obtain        the same structure of materials probably because of low flux of        the carbon ions (100 times lower than in various embodiments of        the invention) and his process was not pulsed.    -   4. Then there is a relaxation time (between pulses) when the        internal stress generated within the film due to the        sub-plantation is relaxed. This is a temperature-dependent        process and in our case the temperature is <60 degrees C.    -   5. Next pulse comes in at least 100 us after all the processes        in the film are finished

The overall process can be imagined as implanting carbon ions with highenergy inside the film, the film thus growing from inside. This processof the material formation can be considered as the formation of carbonmaterial with exceeding energy brought with the carbon ions. The energyof the ions goes into the formation of a crystal stricture whichpreferably should have as much internal energy as possible. Structureswith high surface area usually have more internal energy, hence thefavourable structure obtained with the high-energy and high-intensityion beam should have a morphology with a high surface area. The presenceof spa bonds suggests additional way to accommodate the high internalenergies per carbon atom.

Example 12—Conductivity of Carbon Material Deposited on Glass

The conductivity of carbon material films deposited over glass atvarious thicknesses was investigated. Samples A to H were preparedaccording to the general method outlined above by depositing carbon ontoa glass substrate according to the general method of Example 1 with apulse energy of 4.5 J. The carbon layer thickness and the depositionprocess parameters were varied between the samples.

Resistance and resistivity were determined with a 2-point probe methodusing a Keithley 2002 multimeter.

The properties of samples A to H are shown in Table 3 below.

The conductivity and resistivity of the carbon material films was foundto be dependent upon the thickness that corresponds to the number of VDCpulses applied to form the film.

TABLE 3 Nμmber of Resistance Resistivity Conductivity Example pulses(×1000) (MΩ) (Ω · m) (S/m) A 25 25.94 0.99769 1.00231303 B 50 7.3200.56308 1.775956284 C 100 1.800 0.27692 3.611111111 D 150 0.828 0.191085.233494364 E 10 29.72 0.57154 1.749663526 F 30 3.810 0.219814.549431321 G 70 0.656 0.08831 11.32404181 H 260 0.269 0.124158.054522924

The conductivity of the carbon material film is due to the sp² bondswhich can be metallic type for net W carbon allotrope, semi-metallictype for graphene or graphite, while the diamond bonds sp³ favour anon-conductive material behaviour. The conductivity can be improved withuse of metal doping.

Example 13—Free Standing Carbon Materials

In samples I to K relatively thick (>200 nm) carbon material films wereseparated from their substrates to provide a free-standing carbonmaterial film. In each case, deposition of the carbon material film wascarried out according to the general method outlined above, and then thefilm was mechanically separated from the substrate. Example J wascarried out with a polyethylene terephthalate (PET) substrate onto whicha thin film of stainless steel was deposited prior to the deposition ofcarbon. The deposition process parameters and substrates used in eachsample are shown in Table 3 below.

TABLE 4 Nμmber of Approx. pulses thickness Example (×1000) (nm)Substrate I 50 800 Stainless steel J 30 500 Stainless steel on PET K 50800 Stainless steel

SEM images showed the bottom side of the free-standing films to besmooth; similar to the smoothness of the stainless steel foil substrateto which is was previously attached. FIG. 12 shows the top side of thefree-standing film was rough, similar to the roughness observed in theSEM images of the film adhered to an aluminium substrate.

FIG. 13 shows a comparison of the Raman spectra of Examples I to K (topline: example I; middle line: example J; bottom line: example K) takenfrom the upper side. The Raman spectra of the upper side of all threespectra has a signal at D: 1350 cm⁻¹ and G: 1580 cm⁻¹ of the carbon.Also there are peaks in the area between 200-1100 cm⁻¹ that thatsuggests the presence of some of the removed substrate materialintegrated into the carbon film. This confirms the formation of strongbonds between the film and the substrate.

Example 14: Doping/Mixing with Iron

A strip of iron-doped carbon-containing material was prepared with agradually increasing gradient of iron content along the length of thestrip, as shown in FIG. 14 .

In order to prepare the strip of carbon material doped/mixed with iron,a vacuum chamber was set up having a first VCD source with a graphitetarget (deposition process was the same as the sample I of example 11)and a second VCD source with an iron target. The iron target was ablatedin such a way that the ablated iron material arrived at the samealuminium substrate as the ablated carbon.

The experiment was initially performed with independent control of thesecond VCD source so that the parameters of the ablated iron plasmacould be adjusted to provide the required different energies, timing ofpulses, densities etc of the iron ions arriving at the substrate. Thisallowed the structure and abundance of dopant material to be preciselycontrolled. The pulses of carbon and other material plasmas can bearranged to arrive at the substrate simultaneously, alternating pulse bypulse, or alternating a number of pulses of the first material and thena number of pulses of the second material.

The iron-doped carbon material was prepared such that the centre ofdeposition of carbon was towards the left side of the as strip, whilstthe centre of deposition of iron was on the right of the strip. Hence,the iron-doped material was prepared in such a way that there was agradual increase in carbon content and a gradual decrease in ironcontent from left to right across the strip.

Raman analysis was performed on three different areas of the strip ofiron-doped film prepared above, as shown in FIG. 15 a and FIG. 15 b .Area 1 of the strip (on the far left of the strip) corresponds toapproximately 90% iron and 10% carbon film. Area 2 of the strip (in thecentre of the strip) corresponds to approximately 50% iron and 50%carbon film. Area 3 of the strip (on the far right of the strip)corresponds to approximately 10% iron and 90% carbon film. The Ramanspectra confirmed the abundance of material in each area of the strip.

For Fe samples, Fe peak intensity increased as the thickness increased.For C samples, all samples showed a crystalline and amorphous mixedstructure.

FIG. 16 a shows XPS analysis of the carbon content in areas 1, 2, and 3of the strip. There is a noticeable shift in the character of the carbonbonds from sp³ to sp² as the carbon content of the strip increases. FIG.16 b shows XPS analysis of the iron content in areas 1, 2, and 3 of thestrip.

In conclusion, this study demonstrates the possibility of dopingcarbon-containing films with iron. This technology can be used to dopecarbon-containing materials with any other material.

Example 15: Battery Test

Electrodes were formed by depositing carbon material (0.1 mg) onstandard copper over an area of about 1.13 cm² without any additionalmaterial interlayers, i.e. the carbon material was deposited directlyonto the copper foil.

The deposition conditions for the carbon material were the same assample 6 of Example 3.

The electrochemical properties of the electrodes as anodes in lithiumion cells were investigated using 2032-type coin cells with a lithiumfoil counter electrode and 1M LiPF₆ in ethylene carbonate/dimethylcarbonate (EC/DMC) (1:1 v/v) as the electrolyte, and separator [Celgard25 μm Trilayer polypropylene-polyethylene-polypropylene membrane].

The specific capacities of the electrodes were calculated from the totalmasses of active materials, and their electrochemical characteristicswere examined by charge-discharge curves using a galvanostat (CT2001A,LAND) within a 0.01-3 V range.

An electrochemical test of the coin cell test battery with the carbonmaterial on copper electrode was performed over 200 cycles. FIG. 17 ashow the cycleability (˜200 cycles) of the carbon material on copperelectrode. The specific capacity of the 200^(th) cycle was observed tobe 716 mAh/g at a current of 0.5 A/g. This shows that carbon materialhas a higher specific capacity than graphite (theoretical specificcapacity of 372 mAh/g) at relatively high current density and that thiscapacity is stably retained over 200 cycles with insignificant losses.The first cycle capacity of 1700 mAh/g was found to become irreversibleand it is thought that this is related to the formation ofSolid-Electrolyte Interface (SEI) during first 20 cycles. The SEIformation requires further investigation.

With reference to FIG. 17 b , since at full capacity the potentialagainst lithium is zero volts, all available lithium sites appear to beutilised during discharge, which is reproducible even after 200 cycles.

Discussion of Examples 13 to 15

The battery performance of the examined embodiments of carbon materialis postulated to originate from their structure, which defines metal orsemi-metal conductivity, and a Li ion intercalation mechanism betweenthe 2D layers of carbon. It is thought the 2D layers consist of the netW carbon allotrope or other similar to graphene 2D structure whichprovides both the electronic conductivity and an intercalationmechanism. The distance between the 2D layers are slightly larger thanin graphite, providing the space for the Li ion intercalation. Thehierarchical porosity of the carbon materials is also beneficial for thebattery performance.

In summary, the examined carbon materials' benefits for batteries can besummarised as follows:

-   -   1. Crystalline areas with 2D structures which provides metallic        electrical conductivity.    -   2. Larger-than-graphite distance between 2D layer enables higher        capacity of Li ions intercalated into the carbon material.    -   3. Hierarchical porosity of carbon material enhances electrolyte        penetration and increases specific capacity.    -   4. Presence of sp³ bonds improves mechanical hardness of the        carbon material, which enhances cyclability.    -   5. Formation of chemical bonds with the substrate/current        collector improves contact/battery impedance.    -   6. Possibility to dope the carbon materials with materials (Si,        for example which have high specific capacity) which can improve        further the battery performance.    -   7. Possibility to deposit carbon material on the battery        components without use of binder improves further the battery        weight hence improving energy density of the cell.    -   8. Combination of the material conductivity with good        contact/adhesion to the substrate and with the good penetration        of electrolyte into the carbon material through the        hierarchically arranged pores provides a high rate of        charging/discharging currents (up to 10C) of the battery cell.

In conclusion it was found that the carbon material can be used as anelectrode material in batteries or supercapacitors. The application forenergy storage can be achieved with different setups, using differentelectrolytes and/or second electrode materials.

What is claimed is:
 1. A carbon material formed by exposing a substrateto a flux of at least 10¹¹ carbon ions per cm² of substrate per 1 mswhile the substrate is at a temperature of less than 60° C., a majorityof the carbon ions having a kinetic energy of at least 10 eV to providea carbon material comprising sp² and sp³ hybridized carbon.
 2. Thecarbon material of claim 1, wherein the carbon material has ahierarchical porosity to provide a specific lithium storage capacity ofat least 400 mAh/g.
 3. The carbon material of claim 1, wherein thepercentage of sp² type carbon is at least 25 w % based on the totalweight of the material.
 4. The carbon material of claim 1, wherein thepercentage of sp³ type carbon is at least 20 w % based on the totalweight of the carbon material.
 5. The carbon material of claim 1,comprising at least one area with a plurality of regularly arranged,graphene-like layers of carbon and the at least one area is embedded inamorphous carbon.
 6. The carbon material of claim 5, wherein aninter-layer spacing between individual layers in the plurality of layersis greater than 0.335 nm.
 7. The carbon material of claim 1, wherein thecarbon material has an electrical conductivity of at least 1 S/m.
 8. Thecarbon material of claim 1, wherein the carbon material has an initialspecific lithium storage capacity of at least 1000 mAh/g at a firstcharge cycle.
 9. The carbon material of claim 1, wherein the carbonmaterial has a surface area of at least 1000 m²/g.
 10. The carbonmaterial of claim 1, wherein the carbon material comprises from 0.1 w %to 30 w % of one or more additives or dopants, the one or more additivesor dopants comprising an element selected from the group consisting ofSi, P, Fe, Cu, Li, Al, N, O, S, P, B, Ti, Co, Ni, Na, K, andcombinations thereof.
 11. The carbon material of claim 10, wherein theone or more additives or dopants are either co-deposited with the carbonor incorporated into the carbon material as a plurality of particles orlayers.
 12. The carbon material of claim 1, wherein the specific lithiumstorage capacity after 200 charge/discharge cycles is at least 400mAh/g.
 13. The carbon material of claim 1, wherein the carbon materialis formed by physical vapor deposition (PVD).
 14. The carbon material ofclaim 1, wherein the hierarchical porosity comprises a first set ofgrains having a size of between 10 nm and 100 nm, a second set of grainshaving a size of between 100 nm and 1000 nm, and a third set of grainshaving a size of greater than 1 μm.
 15. The carbon material of claim 1,wherein the percentage of sp² type carbon is between 54 w % and 59 w %,and the percentage of sp³ type carbon is between 24 w % and 31 w %. 16.The carbon material of claim 1, wherein the percentage of sp² typecarbon is between 79 w % and 81 w %, and the percentage of sp³ typecarbon is between 7 w % and 9 w %.
 17. A method of making a carbonmaterial, the method comprising: exposing a substrate to a flux of atleast 10¹¹ carbon ions per cm² of substrate per 1 ms while the substrateis at a temperature of less than 60° C., a majority of the carbon ionshaving a kinetic energy of at least 10 eV to provide a carbon materialcomprising sp² and sp³ hybridized carbon.
 18. The method of claim 17,wherein the sp² and sp³ hybridized carbon have a hierarchical porosityto provide a specific lithium storage capacity of at least 400 mAh/g.19. The method of claim 17, wherein the percentage of sp² type carbon isat least 25 w % based on the total weight of the material and thepercentage of sp³ type carbon is at least 20 w % based on the totalweight of the carbon material.
 20. The method of claim 17, wherein thecarbon material comprises at least one area with a plurality ofregularly arranged, graphene-like layers of carbon and the at least onearea is embedded in amorphous carbon.
 21. The method of claim 17,wherein the flux is provided by a virtual cathode deposition (VCD)process.
 22. The method of claim 17, further comprising co-depositingone or more dopants or additives to form part of the carbon material orincorporating the dopant or additives into the carbon material asparticles or layers.
 23. The method of claim 17, further comprisingseparating the carbon material from the substrate to provide afree-standing carbon material film.
 24. The method of claim 17, whereinthe carbon material is deposited on the substrate without any binders toadhere the carbon to the substrate.
 25. The method of claim 17, whereinthe flux is pulsed with a pulsing frequency of between 1 Hz and 20,000Hz, a pulse duration of between 0.1 μs and 1000 μs, and a total energyper pulse of greater than 2.5 J.
 26. The method of claim 17, wherein theflux is provided in a plurality of pulses such that the carbon ionscontact the substrate in less than 50 μs.
 27. The method of claim 26,wherein a relaxation time between each of the plurality of pulses is atleast 100 μs.